Radio apparatus



I. WOLFF RADIO APPARATUS v Dec. 15, 1936.

` Filed oct. s1. 1934 sss ilalleli.

Patented Dec. l5, 1936 UNITED STATES PATENT OFFICE mio APPARATUSDelaware Application October 31, 1934, Serial No. 750,791

19 Claims.

This invention relates to radio apparatus and particularly to a methodof and a device for modulating radio frequency energy of ultra highfrequency.

It is known that a beam of radio frequency energy may be modulated bymodulating an ionized gas through which the beam is projected. In acopending application, Serial No. 687,544, filed August 3l, 1933, byErnest G. Linder, it was shown that gaseous discharge tubes of one typeor another might be interposed in the path of a radio frequency beam formodulating theamplitude thereof. Linders device is an improvement overother modulating systems in that amplitude modulation of ultra highfrequencies may be obtained quite independently oi disturbing effectsupon the carrier oscillator. The amplitude modulation is alsoaccompanied in greatly reduced degree by frequency modulation. It has,however, been found somewhat diiiicult in all cases to obtain suflicientfreedom from objectionable frequency, or phase modulation. The phasemodulation is caused by variations in the index of refraction of thegaseous medium in a single tube through which the radio beam isprojected. The index of refraction, in turn, is a function of certainabsorption and reflection characteristics the importance of which willpresently be discussed.

It is among the objects of my invention to provide modulating means tobe used in connection with an ultra high frequency radio energygenerator, which means shall be relatively free from phase modulationwhen amplitude modulation alone is desired.

It is another object of my invention to provide means of the characterhereinbefore suggested in which frequency modulation may be had to thesubstantial exclusion of amplitude modulation. if such is desired.

A still further object of my invention is to provide an improved methodof and means for modulating ultrahigh frequency radio energy in Y such amanner that 'distortion of the desired signals may be eiectuallyavoided, even when a high percentage of modulation is obtained.

In carrying out my invention, I preferably employ two distinct zones ofionized gas, the characteristics of these zones being so suitablydifferentiated from one another as to compensate for either theabsorption or the refraction effects inherently present in these ionizedzones.

The various objects, features and advantages of my invention will bestbe understood upon reference to the following detailed description whentaken in connection with the accompanying drawing, in which Figure 1shows schematically one embodiment of a radio transmitter having amodulating system comprising a plurality of gaseous discharge devicesfor intercepting the path of a radio beam,

Fig. `2 is a plan view of the gaseous discharge tul'es otherwise shownin perspective in Fig. 1, an

Fig. 3 is another plan view showing a modiiication.

The embodiment of my invention as herein shown for illustrative purposesin Figs. 1 and 2 comprises preferably a generator I adapted to produceoscillations of ultrahigh frequency, the wavelength of which is of theorder of a few centimeters, or less. The oscillations thus generated maybe impressed upon and radiated from an antenna 3. A parabolic reector 5may be 2 used for directing the radio beam in the direction of areceiver (not shown) to which it may be desired to transmit signals.

For intercepting the radio beam and for providing modulations thereof Ipreferably employ a gaseous discharge tube 1 having a thickness a.Another gaseous discharge tube 9 having a thickness b is also employed.The gaseous contents of the tubes 1 and 9 respectively may bedifferentiated from one another both as to kind of gas and as topressure. The voltage impressed across the electrodes of these tubes mayalso be differentiated in the one case from that in the other. For thispurpose the conductors II are connected at diierent points to the sourceof direct current I3 so that the voltage drop in the tube 1 may begreater than that in the tube 9. The connections may also beinterchanged, if desired. Other electrodes of the tubes 1 and 9respectively are connected to the secondary I5 of a transformer Ilhaving a primary which receives energy from any suitable modulator, suchas telephone transmitter I9. The secondarir winding I5 has a mid-tap 2lwhich is connected back to the battery I3 for completing the modulatorcircuits.

It will be noted that the gaseous discharge tubes 'I and 9 are suitablyconnected with the secondary winding I5 for operation in a pushpullmanner.

Because of differences in the absorption and refraction characteristicsof the two tubes 1 and 9, it is possible to obtain amplitude modulationwithout appreciable phase modulation, or vice versa. II amplitudemodulation alone is desired,

then the phase modulation in the tube 1 is caused to neutralize thephase modulation in the tube 9. If frequency or phase modulation isdesired, then the amplitude modulation in the tube 1 is caused toneutralize the amplitude modulation in the tube 9. How this isaccomplished may be best understood by a mathematical consideration ofthe factors involved.

Let f represent the carrier frequency radiated b'y the antenna 3. Theindex of refraction (no) of the unmodulated gaseous medium such as thatin one of the tubes 1 and 9 may be compared with the nal index ofrefraction n when the gaseous medium is subjected to modulation, Let drepresent the length of the ionized gas path (in centimeters) throughwhich the radio frequency beam Vis tobe projected. The time for theradio frequency wave to 'get through this path is:

dna

where c equals the velocity of light. In the case of the tube 9, dbecomes du due to the thickness of the tube as shown, and in the case ofthe time for the ray to get through the tube 1, d becomes da. Ineithercase when the modulation occurs, the time to is changed to VCombiningvthese equations,

' ing voltages.

Thek phase shiftdue to modulation, therefore, equals- 1 T01-n0) y Tfwhich reduces to 4 g-dQ-'l-llo) where A is the wave length in air.

Under practical conditions, assuming that it is desired to transmit aradio frequency beam having a wave length l i=`1 centimeters,

it is quite possible that (nflml-would equal .5,

also d lwould be of the order of 20V centimeters and the phase shiftwith amplitude modulation would amount to somewhere in the neighborhoodof 21|-, which 'would be very apt to produce unbearable distortion ofthesignals in certain types of receivers. Thisphase shift, however, maybereduced to negligible proportions by taking any one or more of a4 numberof steps tending to produce differential'characteristics in vthe twotubes l and 9, whereby the indices of refraction may be caused to differfrom one another in marked degree. v

Thus, the ratio of tube diameters to one another while in the other tubethe absorption fa'ctor would be predominant. If frequency or phasemodulation is the object then the refraction characteristic is made topredominate while the absorption characteristic of the two tubes is madeto neutralize.

Both the absorption characteristics and the index of refraction aredependent to a certain extent upon the nature of the gaseous medium. Ithas been found that a gas changes its absorption and index of refractionfor electromagnetic waves when its degree of ionization is changed.Accordingly, I have found, for example, that the desired differences incharacteristics of the two tubes 1 and 9 may be obtained by employingneon in one and argon in the other. A mercury pressure of .04millimeters has also been found satisfactory. I do not intend, however,to be limited in carrying out my invention to any particular gaseouscontent of the tubes, nor to the Working pressure thereof, as heregiven.

Absorption ofthe radio frequency wave as it passes through the gas iscaused mainly by collisions made by the free electrons with ions,molecules, or against the tube Walls. The effective collision frequencyis determined largely by the kind of gas, the amount of impuritiespresent, and the pressure. Under certain conditions, a small amount ofimpurities may change the factor of collision frequency, and hencechange the absorption factor, many fold.

'I'hc phase change is due primarily to the number of free electrons orion density in the gas. For optimum results it has been found best torst provide suitable differences in the characteristics in the tubes 1and 9 in accordance with the foregoing teachings and th n to vary thedifference of potential applied o these two tubes through the conductorsIl so as to provide suitable compensation between the respective indicesof refraction of the ionized gases therein for substantiallyneutralizing the phase shift caused by one tube in comparison with thatcaused by the other. The optimum conditions may be readily obtained byadjusting the relative ionizing voltages.

It will be clear from theforegoing disclosure that the radio frequencyWave must pass through the tubes 9 and 1 successively. As shown in Fig.1, the two tubes have different voltages impressed thereon. Thesevoltages may, however, be equalized if necessary in order to produceneutralization of phase shift caused by modulation potentials. When thecurrent in one of the tubes is increased, that in the other is decreaseddue to the push-pull arrangement of the circuit connected through thesecondary winding I5. The tubes 1 and 9 themselves beingcharacteristically different, the applied alternating current voltagegenerated in the secondary I5 may be caused to produce amplitudemodulation on the radio beam while the phase modulation is balanced out.

It will be noted that the contra-phasal impress of modulating voltageupon the two tubes 1 and 9 possesses a still further advantage. Ifeither or both of the tubes `is found to possess a non-linear relationbetween the absorption characteristic and the impressed modulatingvoltage, it doesnt matter. The push-pull operation of the two tubescauses the non-linearites themselves to be substantially balanced out.

Referring to Fig. 2, i-t is shown that the path of the radio frequencybeam may be made longer through tube 'I than through tube 9 in order toeffect differences in the degree of absorption. In

.while substantially suppressing phase modulathis case thecross-sectional diameter a is greater than the cross-sectional diameterb. In Fig. 3, however, the same eifect may be obtained while using twotubes of the same cross-sectional diameter. In this case additionalvertical sections are provided and by staggering the sections in twoplanes the effective thickness dimension a, which represents the path ofthe radio beam through the tube 8 is adjusted to a suitable value.

Although I have disclosed herein certain speciflc means foraccomplishing the objects of my invention, these are given merely by wayof-example and are not to be construed as limitations to the scope of myinvention. Other modifications will suggest themselves to 'those skilledin the art, and my invention, therefore, is not to be limited exceptinsofar as is necessitated by the prior art and by the spiritof theappended claims.

I claim as my invention:

1. A radio transmitting system including a carrier wave radiator, aplurality of gaseous discharge devices in the path of radio frequency.

waves projected vfrom said radiator, said devices having differentiatedabsorption and` refraction characteristics, and means for producingamplitude modulation of said radio waves and for simultaneouslyminimizing the phase modulation thereof, said means comprising apparatusfor impressing modulation energy simultaneously upon said gaseousdischarge devices, and contraphasally on two portions thereof.

2. A system in accordance with claim 1 in which the gaseous contents ofsaid discharge devices are chemically differentiated from one another,asbetween respective devices.

3..,A system in accordance withclaim 1 in which the gas pressure in oneof said discharge devices differs from that in another.

4. A system in accordance with claim 1 in which one of the gaseousdischarge devices has dimensions and shape which present a longer pathof travel for said radio waves when projected therethrough than isprovided by another of said discharge devices.

5. 'A system in accordance with claim l and including means forimpressing across the electrodes" of one of said gaseous dischargedevices an ionizing potential greater than that which is applied acrossthe electrodes of another of said devices.

6. A system inaccordance with claim 1 in which one of the gaseousdischarge devices possesses greater ion density than is possessed byanother of said devices.

7. A system in accordance with claim l in which one of said gaseousdischarge devices possesses greater absorption characteristics withrespect to radio frequency wave energy than is possessed by another ofsaid devices.

8. A system in accordance with claim l in which one of said gaseousdischarge devices possesses greater radio frequency wave refractioncharacteristics than is possessed by another of said devices.

' 9. Inra device of the class described, a source Vof radio frequencycarrier Wave energy, a source of signal modulation energy, `a pluralityof gaseous media disposed in the path of said radio frequency carrierwave energy. and means including a push-pull network for so controllingthe ionization of said gaseous media differentially in` response tovariations in said 4modulation energy that amplitude modulation of saidradio frequency carrier wave energy is` obtained tion thereof.

10. In a device of the class described, a source of radio frequencycarrier wave energy, a source of signal modulation energy, a pluralityof gaseous media disposed in the path of said radio frequency carrierwave energy, and means including a push-pull network for so controllingthe ionization of said gaseous media differentially in response tovariations in said modulation energy that phase modulation of said radiofrequency carrier wave energy is obtained while substantiallysuppressing amplitude modulation thereof.

ll. In a device of the class described, a gaseous discharge tube adaptedto be interposed in the path of a directed radio beam for modulating thesame, said tube having non-linear refraction characteristics in relationto variations of ionizing voltage impressed across its electrodes, asecond gaseous discharge tube adapted to be simultaneously interposed insaid path, said tube having non-linear absorption characteristics inrelation to variations of ionizing voltage impressed across itselectrodes, and means for modulating the energy amplitude of said radiobeam in response to modulations of ionizing voltage impressedcontraphasally upon the two said tubes.

l2. In a device of the class described, a pair of gaseous dischargetubes adapted to be interposed in the path of a directed radio frequencybeam for modulating the same, one of said tubes having a greater ratioof absorption of said radio beam per volt of impressed modulationvoltage than the other oi said tubes, each of said tubes having oppositeindices of refraction, and means in combination with said tubes forcontraphasally impressing thereon modulations of an ionizing voltage,whereby the ratio of absorption and the index of refraction isincreasing in the first tube when the index of refraction is decreasingin the other of said tubes.

13. In a radio transmitting system having a source of directed radiofrequency carrier wave energy and a plurality of raried gaseous zonesintercepting the path of said energy, the method of producing amplitudemodulation of said energy which comprises providing suitablydinerentiated conditions of ionization in one of said gaseous zones withrespect to another of said gaseous zones, producing a glow discharge ineach of said zones,lvarying the drop of potential along the path of saidglow discharge in each zone in accordance with a signal by which saidradio frequency carrier wave is to be modulated,`

and simultaneously controlling variations of the absorption and therefraction characteristics in respectively diierent gaseous zones insuch manner that phase modulation of said carrier wave energy issubstantially suppressed.

14. The method of modulating a radio frequency wave which comprisesprojecting the radio frequency wave through a pair of gaseous dischargepaths, changing the absorption characteristic of one of said paths, andcontraphasally changing the index of refraction of the irst and secondof said-paths to said radio frequency wave in accordance with signalcurrents.

l5. The method of modulating a radio frequency wave which comprisesprojecting the radio frequency wave through a pair of gaseous dischargepaths, changing the index of refraction of one of said pairs to saidradio frequency wave, and contraphasaliy changing the absorptioncharacteristics of each of said paths to said Vradio frequency wave inaccordance with signal curren 16. The method of modulating the phase ofa radio frequency wave vwhich comprises projecting the radio vfrequencywave through a pair of gaseous discharge paths, varying the index ofrefraction of one of said pathsv to said radio frequency wave, andcontraphasally varying the absorption characteristics of each of saidpaths to said radio frequency Wavein accordance with signal currents.

17. The method of modulating the amplitude of a radio frequency wavewhich comprises projecting the radio frequency wave through a pair ofgaseous discharge-paths, varying the absorption characteristic of one ofsaid paths to said radio frequency wave, and contraphasally varying theindex of refraction of each of said paths to vsaid radio frequency wavein accordance with signal currents.

18. The method of modulating the phase of a radio frequency wave whichcomprises projecting the radio frequency wave through a pair of gaseousdischarge paths. varying the index of refraction of one of said paths,and neutralizing any change in the absorption characteristic of the lastmentioned path byoppositely varying the absorption characteristic of theother path in accordance with signal currents.

i9. The method of modulating the ampntude 1 of a, radi'o frequency wavewhich comprises projecting the radio frequency wave through a pair ofgaseous discharge paths. varying the absorption characteristic of one ofsaid paths, and neutralizing any change in the index of refraction ofthe last mentioned path by oppositely varying the index of refraction ofthe other path in accordance withl signal currents.

IRVmG worm.-

